Solid propellant technology has evolved around the use of components readily available at the time of development and use. The surplus materials following World War II included gun powder, nitrocellulose, and other explosive ingredients. The availability of these materials motivated research for their use in solid propulsion technology. As these materials were used in solid propellants, the need for stabilizers was recognized. When stabilizers are used in solid propellants, a need is established for monitoring stabilizer chemical changes to ascertain their efficiency in stabilizing the propellant composition.
A patent of interest in the stabilizer technology field, which is assigned to the United States of America as represented by the Secretary of the Army, is U.S. Pat. No. 3,335,185. This patent was issued to Hiram W. H. Dykes on Aug. 8, 1967 and relates specifically to recovery of stabilizers, such as diphenylamine and resorcinol. In the method disclosed by this patent a small propellant sample (e.g., 100 mg.) is first dissolved in a suitable inert organic solvent having a low boiling point, acetone being preferred. The separation of the stabilizers is accomplished by specific materials known as developers in a thin-layer chromatography method. The developers are selected from the normal eluotropic series which is generally made up of a listing of solvents ranging from low polarity to high polarity. The developers are selected from the group consisting of n-hexane, carbon disulfide, carbon tetrachloride, trichloroethylene, toluene, benzene, methylene chloride, chloroform, ether, ethyl acetate, methyl acetate, aceton, n-propyl alcohol, ethyl alcohol, methyl alcohol and water.
Although the above method serves to separate and identify specific ingredients in small amounts, the separation and reclamation of massive amounts of propellant ingredients has not been of major concern since, prior to the use of very expensive specialty ingredients, the normal disposal of hazardous munitions and ingredients centered around open burning and open destruction (OB/OD). However, after environmental controls were implemented, and with expectation of more stringent controls in the future, the need for developing environmentally safe approaches for demilitarization and disposal of surplus and reject propellants, explosives, and energetic materials has become a major driving force.
The advancements of new technologies relating to propellant processing and reclamation of special ingredients from propellants highly loaded with particulate solids are disclosed in co-inventions as follows:
a. Statutory Invention Registration, Reg. Number H273, published on May 5, 1987, discloses "Processing of High Solid Propellant" by William S. Melvin and Porter H. Mitchell. This process relates to mixing of high solids loaded composite propellants at reduced viscosity by employing near critical liquid (NCL) carbon dioxide (CO.sub.2) as a carrier fluid in a volume amount from about 10 to about 20 percent of the volume of the propellant ingredients. A typical composite propellant contains about 88 percent solids by weight, comprised of ammonium perchlorate, aluminum powder, ballistic modifiers, bonding agent, and about 12 percent liquid ingredients by weight, comprised of liquid polymers, plasticizers, and curatives.
b. Statutory Invention Registration, Reg. Number H305, published on Jul. 7, 1987, discloses "Demilitarization of High Burn Rate Propellant containing Ferrocene of its Derivatives" by William S. Melvin and Porter Mitchell. This invention accomplishes removal of about 99.8% to 100% of ferrocene or its derivatives (e.g., Catocene) from composite propellant which is undergoing demilitarization. After recovery of the high dollar value catalyst material, the propellant can be handled more safely during further processing using various ablation and/or mechanical methods to cut, remove, and comminute the propellant from a rocket motor case, for example, after which reclamation of other specific propellant ingredients can take place.
c. U.S. Pat. No. 4,854,982, issued on Aug. 8, 1989, discloses "Method to Demilitarize, Extract, and Recover Ammonium Perchlorate from Composite Propellants Using Liquid Ammonia" by William S. Melvin and James F. Graham. This method removes substantially 100% of the ammonium perchlorate (AP) from composite propellant in high purity. When large rocket booster units employing thousands of pounds of composite propellant are required to be demilitarized, an environmentally acceptable method is now available to recover a marketable product, ammonium perchlorate oxidizer, from the surplus propellant. This method recycles ammonia following extraction of the AP from the propellant. Recovering the AP from the liquid ammonia during liquid.TM.to-gas phase change may be accomplished using standard industrial chemical ingredient processing equipment such as crystallizers, rotary evaporators, and spray driers. Spray drying is a process whereby AP oxidizer is released in predetermined particle sizes based on liquid droplet sizes and rate of pressure change at a specified temperature. Following this phase change for recovering the AP, the gaseous ammonia is filtered, dried, and compressed to liquid ammonia for recycle/reuse within a closed system.
d. U.S. Pat. No. 4,909,868, issued on Mar. 20, 1990, discloses "Extraction and Recovery of Plasticizers From Solid Propellants and Munitions" by William S. Melvin. This method is directed to extracting and recovering plasticizers and their stabilizers from solid propellant, explosive, and pyrotechnic (PEP) source compositions in which the method employs either NCL or supercritical fluid (SCF) CO.sub.2 as the solvent. The extraction and ingredient recovery method provides an environmentally acceptable alternative to traditional OB/OD of PEP source compositions. CO.sub.2 solvent is nontoxic, nonflamable, noncorrosive, inexpensive, and does not generate any additional toxic or hazardous wastes. The CO.sub.2 solvent is chemically inert when it is confined, pressurized, and/or heated in direct contact with PEP ingredients and compositions. CO.sub.2 gas readily undergoes a NCL gas-to-liquid phase change when confined at a pressure of 831 psig or greater at ambient temperature. By further increasing the pressure and temperature of NCL CO.sub.2 to 1058 psig and 31.3.degree. C. or greater, respectively, SCF conditions of CO.sub.2 are obtained. Either NCL or SCF CO.sub.2 has the capability to be a selective solvent for soluble plasticizers (e.g., nitroglycerin (NG)) and their stabilizers (e.g., diphenylamines and nitroanilines) from nitrocellulose (NC) double base and crosslinked double base PEP materials. All undissolved (insoluble) propellant and munition ingredients are filtered and separated from the NCL or SCF CO.sub.2 solvent prior to the pressure reduction/volume expansion recovery cycle. The recovery of soluble plasticizers and stabilizer from a NCL or SCF CO.sub.2 solvent system is achieved by allowing the NCL or SCF solvent to undergo pressure reduction and phase change to the gaseous state. The gaseous CO.sub.2 is then recycled for additional use in the method.
The employment of detonable, class 1.1 solid propellants by the military services has introduced additional complexities for achieving environmentally safe, rocket motor demilitarization and recovery of specific propellant ingredients for potential recycle/reuse in commercial and military products. Minimum signature, class 1.1 solid propellants typically contain the nitramine oxidizers cyclotetramethylenetetramitramine (HMX) and/or cyclotrimethylenetrinitramine (RDX), nitratoester plasticizers, chemical stabilizers, and a polymer binder. Smoky, class 1.1 propellants may additionally include AP oxidizer and aluminum (AL) metal fuel ingredients.
In July 1989, the U.S. Senate Armed Services Committee directed the establishment of a consolidated solid rocket motor demilitarization research and development program. The program goal is to dispose of large rocket motors in an economical, safe, environmentally acceptable, and reliable manner.
In response to national environmental policy goals established by the Resource Conservation and Reclamation Act (RCRA) and the Department of Defense mandate to minimize the generation of hazardous wastes, the U.S. Army Missile Command (MICOM) successfully explored applications of NCL and SCF technologies for solid rocket motor demilitarization and propellant ingredient recovery. Initial investigations examined the use of ammonia, carbon dioxide, and nitrous oxide as nontraditional extraction solvents for the recovery of ingredients from various PEP materials. These evaluations confirmed that specific liquefied, compressed gases were fully capable of dissolving a variety of PEP ingredients. By applying critical fluid (CF) technologies currently used by chemical processing and manufacturing industries, the recovery of valuable ingredients was demonstrated for PEP materials at the bench-scale. MICOM research resulted in an earlier patent issued to applicant which demonstrated that liquid ammonia at ambient temperature is a super-solvent for dissolving and separating AP, the principal oxidizer in class 1.3 composite propellants, from the insoluble AL/polymer binder components. Evaporation of the liquid ammonia solvent by pressure reduction provides a direct method for recovering the dissolved AP oxidizer and the AL/polymer binder propellant components. Because the critical fluid demilitarization process intentionally avoids the use of water as a propellant processing solvent, the generation of large amounts of contaminated waste effluents are avoided. This aspect provides the critical fluid demilitarization process with major environmental advantages over water-based processes that are less efficient and more energy consuming.
The above extensive review of background information teaches that significant progress has been made of achieving environmentally safe PEP demilitarization. The liquid ammonia rocket motor demilitarization process provides an environmentally safe method for demilitarizing class 1.3 AP composite propellant rocket motors with added benefits of ingredient recovery and hazardous waste minimization. Valuable AP oxidizer, AL polymer binder fuel ingredients, and motor hardware components are recovered for potential recycle/reuse. There remains a need for a similar process for the environmentally safe demilitarization of both minimum signature and smoky types of class 1.1 solid rocket motors and propellants.
The need for demilitarization and recovery of ingredients in 1.1 solid propellants is recognized; therefore, an object of the invention is to provide a method for ingredient recovery and hazardous waste minimization for hazard class 1.1 solid propellants.
A further object of this invention is to provide a method for dissolution, separation, recovery, and reclamation of valuable ingredients from minimum signature 1.1 propellants including smoky 1.1 solid rocket propellants which employ 1.3 solid propellant ingredients.
A specific object of this invention is to provide a method for dissolution, separation, recovery, and reclamation of HMX, RDX, AP, and AL/binder from 1.1 propellants and including 1.1 solid rocket propellants which employ 1.3 solid propellant ingredients.